void LayoutMultiColumnFlowThread::layoutColumns(SubtreeLayoutScope& layoutScope)
{
// Since we ended up here, it means that the multicol container (our parent) needed
// layout. Since contents of the multicol container are diverted to the flow thread, the flow
// thread needs layout as well.
layoutScope.setChildNeedsLayout(this);
m_blockOffsetInEnclosingFragmentationContext = enclosingFragmentationContext() ? multiColumnBlockFlow()->offsetFromLogicalTopOfFirstPage() : LayoutUnit();
for (LayoutBox* columnBox = firstMultiColumnBox(); columnBox; columnBox = columnBox->nextSiblingMultiColumnBox()) {
if (!columnBox->isLayoutMultiColumnSet()) {
ASSERT(columnBox->isLayoutMultiColumnSpannerPlaceholder()); // no other type is expected.
continue;
}
LayoutMultiColumnSet* columnSet = toLayoutMultiColumnSet(columnBox);
layoutScope.setChildNeedsLayout(columnSet);
if (!m_columnHeightsChanged) {
// This is the initial layout pass. We need to reset the column height, because contents
// typically have changed.
columnSet->resetColumnHeight();
}
// Since column sets are regular block flow objects, and their position is changed in
// regular block layout code (with no means for the multicol code to notice unless we add
// hooks there), store the previous position now. If it changes in the imminent layout
// pass, we may have to rebalance its columns.
columnSet->storeOldPosition();
}
m_columnHeightsChanged = false;
invalidateColumnSets();
layout();
validateColumnSets();
}
bool LayoutMultiColumnFlowThread::recalculateColumnHeights()
{
// All column sets that needed layout have now been laid out, so we can finally validate them.
validateColumnSets();
if (!m_needsColumnHeightsRecalculation)
return false;
// Column heights may change here because of balancing. We may have to do multiple layout
// passes, depending on how the contents is fitted to the changed column heights. In most
// cases, laying out again twice or even just once will suffice. Sometimes we need more
// passes than that, though, but the number of retries should not exceed the number of
// columns, unless we have a bug.
bool needsRelayout = false;
for (LayoutMultiColumnSet* multicolSet = firstMultiColumnSet(); multicolSet; multicolSet = multicolSet->nextSiblingMultiColumnSet())
needsRelayout |= multicolSet->recalculateColumnHeight();
if (needsRelayout)
setChildNeedsLayout(MarkOnlyThis);
m_inBalancingPass = needsRelayout;
return needsRelayout;
}
